Browsing by Subject "Adipocytes"

Now showing 1 - 3 of 3
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    Biochemical and functional characterization of fatty acid transport proteins.
    (2009-07) Wiczer, Brian Michael
    The adipocyte fatty acid transport proteins (FATPs), FATP1 and FATP4, have been implicated in both lipid influx and storage and understanding their role in adipose tissue would gain insight into the persistence of metabolic disorders, such as type 2 diabetes. FATP1 was previously determined to be an acyl-CoA synthetase and work described in this thesis additionally explored the acyl-CoA synthetase activity of purified FATP4. FATP4 was found to be a more robust acyl-CoA synthetase than FATP1. Through the use of RNAi in cultured adipocytes, silencing the expression of either FATP1 or FATP4 results in cellular phenotype demonstrating improved insulin responsiveness. Interestingly, silencing FATP1 abolished insulin-stimulated long-chain fatty acid (LCFA) influx, whereas silencing FATP4 had no effect on LCFA influx despite its higher activity. Furthermore, the expression of FATP1 was demonstrated to be important for the activation of the AMP-activated protein kinase during insulinstimulated LCFA influx. In addition to the cytoplasmic localization of FATP1, it was also found to exhibit mitochondrial localization. Further analysis demonstrated a novel role in the regulation of TCA cycle function and mitochondrial energy metabolism, in part, through the interaction of FATP1 with the 2-oxoglutarate dehydrogenase complex, a rate-limiting step in the TCA cycle. This work shines light on how FATPs may play broader roles in metabolism that previously appreciated and the potential implications associated with such roles.
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    The Role of Inflammation and Oxidative Stress in Adipocytes in the Development of Insulin Resistance
    (2015-08) Burrill, Joel
    Inflammation plays a critical role in the pathology of obesity-linked insulin resistance and is mechanistically linked to the effects of macrophage-derived cytokines on adipocyte energy metabolism, particularly that of the mitochondrial branched chain amino acid (BCAA) and tricarboxylic acid (TCA) pathways. To address the role of inflammation on energy metabolism in adipocytes we utilized high fat fed C57Bl/6J mice and lean controls and measured down regulation of genes linked to BCAA and TCA cycle metabolism selectively in visceral but not in subcutaneous adipose tissue, brown fat, liver or muscle. Using 3T3-L1 cells, TNFα and other pro-inflammatory cytokine treatments reduced the expression of genes linked to BCAA transport and oxidation. Consistent with this, [14C]-leucine uptake and conversion to triglycerides was markedly attenuated in TNFα-treated adipocytes whereas conversion to protein was relatively unaffected. Since inflammatory cytokines lead to induction of ER stress, we evaluated the effects of tunicamycin or thapsigargin treatment of 3T3-L1 cells and measured a similar down regulation in the BCAA/TCA cycle pathway. Moreover, transgenic mice overexpressing XBP1s in adipocytes similarly down regulated genes of BCAA and TCA metabolism in vivo. These results indicate that inflammation and ER stress attenuate lipogenesis in visceral adipose depots by down regulating the BCAA/TCA metabolism pathway and are consistent with a model whereby the accumulation of serum BCAA in the obese insulin-resistant state is linked to adipose inflammation.
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    Unconventional protein secretion from adipocytes
    (2018-10) Josephrajan, Ajeetha
    Endocrine function of the adipose tissue plays a major role in maintaining energy balance and glucose homeostasis by releasing a large number of bioactive proteins. Any dysfunction of the endocrine function of the adipose tissue caused due to obesity will initiate pathophysiological changes and hasten disease progression. In this thesis, I focus on the secretion of leaderless proteins from the primary cells of the adipose tissue, the adipocytes. This secretion process is called unconventional protein secretion (UPS) and as shown here for the first time, our results indicate that the UPS is highly regulated and a variety of proteins are secreted upon the adipocyte receiving a lipolytic stimuli. To characterize the UPS, we followed the secretion pathway of unconventionally secreted adipocyte fatty acid binding protein (FABP4). FABP4 is one of the majorly expressed protein in mature adipocytes whose intracellular function is lipid storage and trafficking. Increasing evidence indicates that FABP4 has multiple functions extracellularly and is strongly associated with metabolic disease progression. Our results elucidate the regulation and mechanism of UPS/FABP4 secretion pathway. Unraveling the role of UPS proteins in the circulation and integrating them as a systemic response will be central to our understanding of the balance between healthy and unhealthy states. Such a study will be more insightful in predicting metabolic diseases than analyzing different individual marker proteins in the blood stream at a time for various pathologies.